The need for converting signals can be shown, by way of example, in machine tool and position indication applications. Encoders (i.e., rotational, linear etc.) are used to indicate a position of a work piece or a machine part. It is often necessary, however, to convert the output of the encoders (or position indicators) from their fixed number of indicia per unit (e.g., fixed number of indicia per unit of rotation, fixed number of indicia per unit of length, or otherwise) to a number of indicia per unit that corresponds to some aspect of the work piece or machine tool position.
Industry standard rotary shaft encoders, for example, are manufactured with many different numbers of counts per revolution (i.e., many different resolutions) in an attempt to cover the mechanical and precision needs of machine tool position indication applications. However, the resolutions are limited to integer values, i.e., whole numbers of counts per revolution, leaving a user to select only a close match, rather than the precise number of counts per revolution desired, and then to use custom gear trains, or complex processor-based computational conversion systems, in order to obtain a desired number of counts per revolution.
For example, to generate a converted output comprising a count, i.e., a pulse, every 0.5000 inches on the perimeter of a 25.000 inch diameter drum, and whose shaft is mechanically coupled to a 1120 count per revolution, i.e., pulse per revolution, rotary shaft encoder, it is necessary to convert the pulse output of the rotary shaft encoder from a whole number of pulses per revolution to a non-integer number of pulses per revolution.
At the same time, however, for machine tool applications, the converted output must be accurate at various, and varying rotational speeds, and accommodate reversals in direction as, for example, the drum is rotated forward and backward at various and varying speeds.
U.S. Pat. No. 6,789,041 (by the same inventor as the present specification) discloses a converter for receiving an input signal that includes indicia corresponding to a distance, in time or position, and for generating a converted, output signal, so that the input signal is a non-integral multiple of the output signal. This patent is incorporated herein by reference in its entirety. The converter includes a plurality of dual-value, up-down counters that convert a bi-directional input signal into a bi-directional output signal. The counters are chained together and operate in a cascading fashion to provide the output signal. Coefficients that are a function of the non-integral multiple are assigned to each of the plurality of counters thus providing one or two upper count limits for each counter.
However with the converter of U.S. Pat. No. 6,789,041, it is assumed that the counter coefficients have been previously calculated and loaded during manufacture of the converter. After having received such a converter from the manufacturer, the end-user is unable to change and load other coefficients in order to use a different input signal/output signal ratio. Rather, the end-user is required to purchase a different converter or related component when the need arises for a converter having different output ratio. Accordingly, there is a need for a bi-directional signal converter that is field-programmable.